In manufacture of a semiconductor wafer (hereinafter referred to as a wafer) or in device manufacture using a wafer, an end portion (edge portion) of the wafer might be damaged or chipped by contact with another component or a wafer holding member. Moreover, the wafer might be split off due to the damage or chipping. The damage or chipping can be caused easily in an end portion of a wafer probably because of a shape of the wafer end face (so-called edge profile portion). Thus, it is important to correctly measure the edge profile of a disc-shaped measurement target represented by a wafer. The shape of the end face here refers to a profile in a thickness direction of the wafer (one dimensional direction), that is, a shape of a section in the thickness direction and hereinafter referred to as an edge profile.
A typical example of the measurement method of the edge profile is a nondestructive test method (SEMI-MF-928-0305 standard Method B) defined by Semi Standard, which is a standard determined by an industrial organization for semiconductor manufacturing devices/materials, Semiconductor Equipment and Materials International (hereinafter referred to as SEMI). In this nondestructive test method, light is projected to a chamfered end portion of a disc-shaped wafer from a direction substantially parallel to each face of the front and back sides of the wafer (first direction), a projection image of the wafer end face is picked up by a camera from a direction opposite the light projecting direction, and the shape of the wafer end face is measured on the basis of the projection image (hereinafter referred to as a light projection measuring method). An outline of the projection image obtained by the light projection measuring method represents a sectional shape of the wafer end face (shape of a section cut off in the thickness direction).
For example, Patent Document 1 proposes prevention of blurring of an outline or occurrence of a diffraction fringe in the projection image by having outgoing light of a point light source pass through a collimator lens and collimated (made into parallel light) and by projecting the light flux to the measurement target in the light projection measuring method.
As mentioned above, in order to make shape measurement with accuracy by the light projection measuring method, a light flux parallel to each face of the front and back sides needs to be projected to a plate-shaped measurement target.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-145487